Pass Laboratories XA200.8 monoblock power amplifier

It was almost seven years ago that Nelson Pass, whose talks and exhibits I'd covered at many a Bay Area Burning Amp DIY event and audio show, surprised me with a loan of two Pass Laboratories' XA 160.5 class-A monoblock amplifiers. Ten months later, after I'd commented that my system had challenged the XA 160.5s in the bass department, he sent me a pair of XA200.5 monos. I connected those bigger babies to Wilson Audio Sophia 3 loudspeakers and some now-discontinued digital components with Nordost Odin 1 interconnects and speaker cables. Then came my way, toward the end of 2016, the XA200.8 monoblocks ($42,000/pair).

My joy at the arrival of the solid-state XA200.8s was tempered by their weight, which seemed only to increase with time. In fact, a day after we removed them from our amp stands and packed up one to ship to John Atkinson to be measured, I was wearing a back brace and moving with care. Thank goodness for chiropractors.

That joy was also tempered by the fact that two XA200.8s consume lots of power even at idle, and put out enough heat to require air-conditioning in spaces where music through open windows might disturb neighbors. The spouse, on receiving our electric bill, has more than once complained about my leaving the amps on for long periods.

However . . .

Description
The XA200.8 measures 19" wide by 11" high by 27.5" deep and weighs 157 lb. Except for a bottom plate of heavy-gauge steel, its case is made of extruded, machined aluminum, with extra-large, side-mounted heatsinks to dissipate the energy of the output stage, which is deeply biased into class-A. A decorative faceplate of thick aluminum, available in silver or black, is dominated by a single large, blue-lit analog meter showing the bias current that includes a tiny Standby LED that glows a brighter blue. When the amp is fully on, the Standby LED goes dark and the meter glows.

Below the meter is a large On button, which complements the master power toggle on the rear panel. (That toggle also serves as a thermal magnetic circuit breaker.) Also on the rear panel are: balanced (XLR) and single-ended (RCA) inputs; widely spaced pairs of locking speaker binding posts whose big tabs make them easy to tighten; an IEC power-cord inlet; a white Signal Ground terminal intended solely for active subwoofers; two binding posts labeled "12V External Turn-on"; and handles for lifting. Thank God for those handles.

Once I'd got these very heavy amps positioned on our Grand Prix Audio Monaco standsthey need a good amount of space to dissipate all that heatsetup was easy. Because I use balanced interconnects, there was no need to insert the supplied gold shorting pins into the XLR input sockets' negative and ground holes (1 and 3). (A little stencil on the rear panel illustrates how to correctly insert the shorting pins.) After the speaker cables were connected in correct polarity, and carefully separated from the interconnects and power cord, I was ready to go.

The XA200.8 requires an hour to fully warm up, and that hour made a huge difference in the sound. Long ago, I owned a Pass Labs Aleph 30 stereo power amp. (I wish I still did, now that I finally have a front end good enough to let me fully appreciate its gifts.) One evening, I brought home a new friend who, on seeing my system, immediately wanted to hear music. I explained that the electronics wouldn't sound good until they'd fully warmed up, but nonetheless put on an LP of Otto Klemperer's recording of Brahms's A German Requiem.

Thirty-five minutes later, in the middle of a grand chorus, the soundstage suddenly went whoomeverything opened up. What before had sounded somewhat small, flat, and colorless seemed to double in size as it blossomed with color and radiance.

"What was that?" my guest asked, somewhat shocked.

"The amps just reached an internal temperature of 125°," I said with a knowing smile.

Nelson Pass may be remarkably open and generous in sharing experimental designs, and even old product casings, with do-it-yourselfers, but he keeps the details of his commercial products close to his vest. As he explains in the XA200.8's owner's manual, "Since the release of the X.5 series . . . we began working on what has now become the X.8 amplifiers. They embody everything we know, and while I can't divulge all the details, I can tell you about some things which might interest you."

Among those things: Each XA-series model is unique, with sonic characteristics determined by its number of devices, heatsinking, supply voltage, bias currents, and output-stage transfer curves. The XA200.8's DC-coupled front-end circuit contains its input and voltage gain stages, and uses a mix of four each of complementary, discontinued Toshiba JFET, MOSFET, and bipolar devices. The only capacitors are across the shunt-bias regulators and in the power supplies. Those supplies, larger than in the .5 series, include additional RF filtering in the AC primary circuits, paralleled fast/soft rectifiers, and very large, toroidal Plitron transformers.

Pass prefers to answer questions by e-mail; I sent him a bunch. In describing his goals and process in moving from the .5 to Xs to .8 series, he wrote:

The two-box Xs 300 came first, and in many ways the rest was the key turning in the lock. Since any hardware differences will affect the sound, we see a series of compromises between cost, power, size, consumption. We made the hardware bigger. The banks of output power MOSFETs already being overkill, we concentrated on the power supplies and the heatsinks. This allowed greater bias current for greater class-A operation into lower impedance loads, which improved performance at lower power levels as well. The weight is almost entirely chassis, heatsinks, and power-supply transformer.

The lesson of the Xs and SIT amplifiers was that a small amount of second harmonic of a particular phase character gives a desirable sonic result. To get that effect, we altered the arrangement of the constant-current sources in the output stage to better duplicate the sound of the Xs output stage. While the .8 amplifiers still have low distortion, they do not suppress second harmonic as much as the .5 series, giving a mostly second-harmonic character at ordinary listening levels and segueing into third harmonic at higher power.

The front end was altered to let the input stage operate with CFA-type feedback instead of VFA. VFA is where feedback is introduced through high-impedance networks, and CFA is an alternative approach with low-impedance networks. The terms VFA (voltage feedback amplifier) and CFA (current feedback amplifier) are misnomers, as both types actually have voltage feedback. As with the Xs, it sounded a little better.

By the time I left ESS. I was convinced that the best path was Bart Locanthi's dictum: An amplifier should be designed for low distortion and wide bandwidth without feedback. Negative feedback is then added to make an already good design perform even better; it is not used to 'clean up' problems in the basic design.

Sound
I've now spent so many hours listening to the XA200.8s alone and comparing it with other amplifiers that I know their sound inside out. When some members of the Pacific Northwest Audio Society commented, after an extended listening session, that they preferred the "organic" sound of the XA200.8, they were on to something.

So with a S/N of 88.2 dB for the audible bandwidth, this amp has less than 15 bits of dynamic range ref. to 1W into 8 ohms. I'm not trying to be contentious, just trying to get this straight in my head. We don't know what the S/N is for full output power, correct?

We do not know the noise at the full power but we know the THD at full power. In fact, if we have 1% THD, we have 7 bits. But we must to be rational to see the truth: at this power(258w in 8ohm), how many bits will you hear ? Which will be the "THD level" of the room ? In fact, each criterion taken separately does not tell us how nice music will sound. Listening the tested device at home is a must.

Mr. Atkinson, I wrote a question for you under another review which I think escaped your attention, and might be of interest to some other readers--I'd greatly appreciate it if you could reply now:

I'm interested in using either the M32 or the M22--driven directly from an NAD M51--to drive a pair of Dynaudio Special 40s. Could you possibly comment on any difference in sound quality? I understand that the power output would be different, and that one is an integrated and one is a power amp. What I'm interested in, mostly, is the difference in sound between the Hypex N-core of the M22 and the different system used in the M32.

I'm interested in using either the M32 or the M22--driven directly from an NAD M51--to drive a pair of Dynaudio Special 40s.

I know from experience that the M32 does a good job driving the Dynaudio speakers. (I review the Special 40s in our September issue.) But as the M32 has a DAC and you already have the M51, the M22 might better suit your needs.

Mr. Atkinson, I think my question was very clear: "the difference in sound between the Hypex N-core of the M22 and the different system used in the M32." I think this would be a question of interest to many readers, and I hope maybe you'll discuss it in the future. Thanks, LTL

Do you understand you are trying to compare an analog power amplifier with a pwm direct digital integrated? It is like comparing an engine to a car as the preamplifier and dac the m22 requires will influence the sound to a great degree.

My opinion is that the architecture utilized in the m32 is the better move for most users.

Thanks for your reply. My understanding was that the M22 is based on the Hypex N-core, which is a PWM module, and that the M32 is also PWM, as you note, so I'm not sure I understand why you call only one of them "analog." Of course I understand that the pre-amp and DAC will influence the sound.

Could you please expand on why you think the M32 architecture is better?

I'm also considering the PS Audio Stellar M700. Like the NAD m22, I would connect the PS Audio monoblocks directly to the NAD DAC, which has variable output.

..that almost all class-a amps I’m aware of are somewhat “soft” in the bass dept. Truth be told – I’m a control freak when it comes to the base; but sometimes I wonder if this whole “tight” thing, as well as the “stage” equivalent etc, does not actually consist another convenient artifact, while my considerable "live experience" does not serve me particularly well.

Since I respect your opinion, could you please rephrase this so I can understand what you're trying to say? What I do know is that, in my listening experience, bass in decent symphony halls and over good club amplification systems is anything but loose, flabby, or of uncertain pitch.

..but in fact is somewhat tautological a thought in the sense of imposing certain preconceptions of “good sound” to reality and consequently using the ensuing real/ideal fusion as a reference point for what "good sound" sould be actually like; I am inclined to call this inevitably circular interaction “the hi-end audio uncertainty principle” :-}

I Googled it .......... The weight of Muhammad Ali when he was the heavy weight champion was 236 pounds .... He was 6 foot 3 inches tall :-) ............. His famous quote "Float like a butterfly, sting like a bee" :-) ..........

This would an interesting situation for comparison with speakers with different impedance 'propensities' than Wilsons. Their size mitigates against easy comparisons!

Also, perhaps all that power conditioning took its toll. Especially with regard to the adjectives about the bass, where that stuff can really turn an amp into an anchor. Did they get a chance to just play plugged right into the wall?

Power 'conditioners' aren't exactly a one size serves all kind of proposition.

It could be cumbersome to get a handle on these monsters in conjunction with the effects of Audience aR2p-TSSOX, Tweek Geek Dark Matter Stealth (with High Fidelity & Furutech options) power conditioners; Nordost QB8, 2 QX4, QK1 & QV2 AC power accessories.

I have owned both the 100.5; the 160.5; the 200.5 and now the 200.8 (A serious case of Audiophile insecurity, perhaps?).
However, I fully concur that the 200.8 is the better amplifier. It surpasses the others in the XA range by far.

... If he were to lower the distortion of his amps to levels similar to that of the Benchmark amp, would he be able to maintain the same subjectively appealing sound quality?

Incidentally, still waiting for reviews of more recent power amps from Rotel. The $1600 (and under 40lbs. for a 2-channel unit) RB-1582 MkII can generate about 250W into 8Ω and 435W into 4Ω, according to the HiFi News test. Peak power into 2Ω is over 1kW.
If you need even more power, the RB-1590 has about double the output at about double the price and weight.

I hope you keep those Amps and use them as your Reference, .10 Cents per Kilowatt hour is pretty much a National Standard, leaving them on will probably cost about $5.00 per day. ( about $1,800 per year ). Port Townsend Air Conditioning is a nonsense thought, you need that Clean Heat from those Amps.!!

Besides, you're not wasting $100,000 Plus +++ on one of those old fashioned 33.3 rigs and all the sundry paraphernalia needed to support the very pricy Vinyl coming to you on a regular basis from Sir. Chad & friends.

Stereophile readership needs you to be a Reference Level person of Integrity, you need those Amps to properly do your job : Being Our Reference Level Audiophile, reporting on all things important ( all things "Stereophile" to me and our man in Oh'Canada ) !

I can only imagine how my recordings of Fischer and Schnabel would sound through a Pass amp like this one. In my cramped Manhattan apt my Klout will have to suffice. Paired with my SME 10, LP12, and modded 1200, I bet it would be magic, notwithstanding the irrelevant comments from some “expert” on analogue’s shortcomings from Michigan, as seen above. Thanks for letting me dream JVS and thanks for an entertaining review.

Your Linn Klout has a rated output of 80W into 8Ω and 160W into 4Ω. According to the Stereophile test, the output of the Pass XA25 reached the clipping point (~1% THD) at 80W into 8Ω and 130W into 4Ω - not much difference. Plus, one two-channel XA25 costs only about one-tenth that of a pair of mono XA200.8 amps and weighs a much more manageable 45lbs.

Does one care more about absolute bass slam than beautiful sound?
And, in a real, live, acoustic setting, does bass slam, or is it a bit soft and unfocused compared to amplified reproduction? I believe it is the latter.

So I for one, could not care less about absolute bass slam or playing music at deafening pressure levels.These are unrealistic ideals imho.

My ears find even Nelson's most modest (power related) efforts (ie: SIT 2, J2) very musically faithful and rewarding in their own way.

Perhaps we have excepted far too poor driver efficiency and poorly engineered impedance curved loudspeakers that demand these enormous power consumers/producers. Should we perhaps look back, and reevaluate our implementation? I think so.

But there will always be those who oppose unnecessary resistance with more power...

These two items should not be used together if one is seeking audiophile approved levels of SQ, especially during a review.

I've yet to find a power conditioner that did not negatively impact music transients, midrange snap, bass slam, bass depth...etc

I've owned some of the audiophile favorites in terms of power conditioners and no matter how bold the claims are from the PC manufacturer that their product doesn't limit current or in some cases believe their product has more power then the wall plug....its all BS.

Even my little Pass XA60.8's are negatively impacted using the well reviewed Shunyata Denali. Same story for the big Torus RM20.

These monster XA200.8's should never be plugged into anything but the wall directly and reviewing them any other way is doing a dis-service to your readers and potential buyers.

JVS...dont let that bad a$$ system of yours go to waste...its time to start De-Tweaking it and let the music flow as intended :)